Barrier coatings and barrier layers are used in a variety of applications; for example absorbent materials, nonwovens, and textiles. They are particularly important in absorbent materials for such products as absorbent pads, medical hygiene products, food bibs, food packaging, table top covers and the like where a hydrophobic layer covers but does not interfere with the absorbent material. The barrier layer prevents the absorbed fluid from penetrating through the side opposite from where fluid was absorbed. When coatings are used on these types of products, it is desirable that they have little or no formaldehyde and no alkylphenol ethoxylate surfactants.
Absorbent materials are frequently multi-layered in construction and can comprise a liquid-permeable cover sheet having one side designed for placement in contact with the wearer or food, an absorbent section, and an impervious backsheet. Polyethylene films are typically used as a backsheet for absorbent pads because it prevents passage of fluids to the opposite side of the film. In some cases, the polyethylene film is perforated in such a way as to allow water vapor to pass through the film but inhibit the passage of fluids. However, there are drawbacks to the use of polyethylene film for absorbent pads. For example, it is sometimes difficult to place and attach the polyethylene film to a substrate, creating waste when it skews off the substrate during secondary operations. In some cases, application of an adhesive, such as a hot melt adhesive, or some other method of attachment is needed to keep the polyethylene film in place. Also, the polyethylene film needs to be applied in a secondary operation which is separate from the production of the absorbent pad, textile, or nonwoven. A more practical substitute for the polyethylene backsheet would therefore benefit the industry.
Examples of coatings used as water repellents are disclosed in the following publications:
Colbert (“Fluorochemicals—fluid repellency for nonwoven substrates” (TAPPI, September 1976, Vol. 59, No. 9, pages 129-131)) discloses the use of fluorochemicals to provide fluid repellency to nonwoven substrates without the formation of continuous film barriers.
U.S. Pat. No. 4,062,818 (Mate, 1977) discloses an aqueous composition which imparts both flame resistance and water repellency properties to nonwoven textiles. The composition contains a poly(vinyl acetate), a chloro- or bromo-substituted phosphate plasticizer, a polyfluoroalkyl polyacrylate, water repellent, and an inorganic, water soluble salt.
U.S. Pat. No. 3,912,674 (Stahl, 1975) discloses a water repellent coating made up of an ethylene ionic copolymer, a paraffin wax, and a terpolymer of vinyl acetate, ethylene, and N-methylol acrylamide. The ethylene copolymer dispersion is held in dispersed phase by means of an amine soap surfactant.
WO98/14078 (Baumann, et al., 1998) discloses a face mask that allows gas to pass through while inhibiting passage of liquid through it. The mask includes a face-contacting layer, an outer cover layer, a polymeric microfiber mat disposed between the face-contacting layer and the outer cover sheet, and a non-woven fibrous mat disposed between the face-contacting layer and the outer cover sheet. The non-woven fibrous mat includes polymeric fibers and a surface energy reducing agent, such as a fluorochemical, a wax, a silicon or a combination thereof.
US 2001/0021616 A1 and U.S. Pat. No. 6,251,210 B1 (Bullock et al, 2001) disclose a method of preparing a stain resistant and water repellant textile fabric in which the fabric is first treated with a fluorochemical textile treatment composition and dried at elevated temperature. The treated fabric is then provided with a polymeric film to one side of the treated fabric and dried again at elevated temperature. A detackifying wax may be part of the secondary treatment composition.